1. Field of the Invention
The invention relates to a strapping machine, more particularly to a strapping machine with a strap tightening unit which is provided with a device to prevent snapping of the strap in case the strapping machine is untimely and accidentally actuated prior to disposing a package in the machine for strapping.
2. Description of the Related Art
Referring to FIGS. 1 to 3, a conventional strapping machine is shown to include a machine body 1, a strap supply reel 11xe2x80x3, a strap feed unit 12, a rotating shaft unit 122, and a strap tightening unit 14.
As illustrated, the machine body 1 defines an accommodating space 111 with a strap guide path 131 and a package-strapping space 112 above the accommodating space 111. The strap supply reel 11xe2x80x3 is mounted on an exterior of the machine body 1. A bundle of strap 11 is mounted on the strap supply reel 11xe2x80x3, and has a leading end fed into the package-strapping space 112 by the strap feed unit 12 via the strap guide path 131 so as to be retained underneath a package support plate 133. The rotating shaft unit 122 is journalled in the accommodating space 111 of the machine body 1, and is formed with a cam unit 123.
The strap tightening unit 14 includes a spring-loaded swing arm 140, and an electrically operated clamp unit 141. The swing arm 140 is mounted pivotally within the accommodating space 11 of the machine body 1, and defines a strap passage to permit extension of the strap 11 therethrough. The swing arm 140 is further associated with the rotating shaft unit 122 via the cam unit 123 in such a manner that rotation of the shaft unit 122 results in turning of the swing arm 140 relative to the machine body 1 along a travelling path from an upper position adjacent to the package-strapping space 112 toward a lower position distal from the package-strapping space 112 so as to perform the strapping operation on the package 2 that is disposed on the package support plate 133, as best shown in FIG. 2. The clamp unit 141 is mounted movably on the swing arm 140, and is movable relative to the strap passage of the swing arm 140 between a clamping position, in which the strap 11 is clamped by the clamp unit 141, and a releasing position, in which the strap 11 is released from the clamp unit 141.
One disadvantage that results during use of the aforesaid conventional strapping machine resides in that in case no package is disposed on the package support plate 133, and the shaft unit 122 is accidentally and untimely actuated so as to move the swing arm 140 to a position between the upper and lower positions for strap tightening operation, snapping of the strap 11 in the strap feed unit 12 will result by virtue of the engagement between the package support plate 133 and the strap 11 (see FIG. 3).
Therefore, the object of this invention is to provide a strapping machine with a strap tightening unit of a simple structure so as to overcome the aforementioned disadvantage that is associated with the conventional strapping machine.
Accordingly, a strapping machine of the present invention includes a machine body, a strap supply reel, a strap feed unit, a rotating shaft unit, and a strap tightening adjustment unit. The machine body defines an accommodating space and a package-strapping space above the package-strapping space. A strap guide path is disposed horizontally in the accommodating space of the machine body adjacent to the package-strapping space. A package support plate is disposed above the strap guide path, and has horizontally spaced opposite left and right sides which extend in a direction transverse to and which span the strap guide path. The strap supply reel is mounted on the machine body, and is adapted to hold a bundle of strap thereon. The strap feed unit is capable of feeding the strap from the strap supply reel to the package-strapping space for encircling the left and right sides of the package support plate via the strap guide path. The rotating shaft unit is journalled in the accommodating space of the machine body, and is formed with a cam unit. The strap tightening unit includes a spring-loaded swing arm, a driving unit, and a micro switch unit. The swing arm is pivoted to the machine body within the accommodating space, and defines a strap passage to permit extension of the strap therethrough. The swing arm is further associated with the rotating shaft unit via the cam unit in such a manner that rotation of the shaft unit results in turning of the swing arm relative to the machine body between an upper position adjacent to the package-strapping space and a lower position distal from the package-strapping space. The clamp unit is mounted movably on the swing arm, and is movable relative to the strap passage of the swing arm between a clamping position, in which the strap is adapted to be clamped by the clamp unit, and a releasing position, in which the strap is adapted to be released from the clamp unit. The driving unit rotates in a first direction for moving the clamp unit to the clamping position, and in a second direction opposite to the first direction for moving the clamp unit to the releasing position. The micro switch unit includes a micro switch which is electrically coupled to the driving unit, a swing lever which is mounted swingeably underneath the package support plate adjacent to one of the left and right sides in such a manner that one end of the swing lever passes over the strap guide path, and an urging member which urges the other end of the swing lever to abut against the micro switch.
In case no package is disposed on the package support plate, and the rotating shaft unit is accidentally and untimely actuated so as to move the swing arm to a position between the upper and lower positions for strap tightening operation, the other end of the swing lever will disengage from the micro switch via the engagement between the strap and the one end of the swing lever. Under this condition, the driving unit is signaled to rotate in the second direction so as to move the clamp unit to the releasing position on the swing arm, thereby preventing snapping of the strap in the strap feed unit.